Recovery of tin from tin ores



Aug. 13, 1935. A. woon RECOVERY OF TIN FROM TIN ORES Filed DeG. 22, 19.35

Patent-ed Aug. 13, 1935' UNITED STATES 7 PATENT oFFicE Y 2,011,533; 'i 'Y Louis Alben wood, London,

British American Mines Limited,

England, 'assilnor to London,

England, a British company Application December 22, 1933, Serial No. 703,631 In Great Britain December 24, 1932 10 Claim's.

This invention comprises improvements in 'or relating to the recovery of tin from tin ores.

It is an object of this invention to facilitate the recovery of tin from tin ores by a chloridization process similar in some respects to that described in United States Patent application Serial No. 627,943 and United States Patent No. 1,931,944 in which tin ores were heated'in admixture with carbonaceous materials and calcium chloride to a temperature of the order of 80()` C. with 'the result that stannouschloride wasevolved from the mixture, was led away as vapour and was separately condensed.

In the present specification the' expression tin ores is intended to include materials on which concentration or like preparatory treatment has been expended and is not limited to the ore as mined. l

Experiments with chloride, other than calcium chloride, in the presence of carbon have shown markedly reduced recoveries of tin which is'.

thought to be due to the fact that during the initial heating stage the chlorides which may beused become volatilized. and lost from the mixture at temperatures lower than those at which the carbonaceous material present effects a reducingvactionv upon the tin ore. Consequently, when the proper reaction temperature for the production of the stannous chloride is reached the other chlorides present may have partially disappeared with adverse results upon the recovery.

Quite apart from the adverse elect upon the recovery in the case ot the use of the more volatile chloridizing agents there is theA risk, when :ferrie oxide is present, of the production lof ferric chlorides which itself is volatile" and may lead to premature'removal offchlorine carrying products.

I have found that in batch treatment of such or if the ore is preheated to the reaction temperature and partially reduced to convert ferric oxide (FeaOs) l which may be present in the ore to ferroso-ferric oxide (FeaOi) then loss of chlorine by evolution and passing away from the ore of ferric chloride or other chlorine carrying products is largely prevented. Even in cases where chlorine carrying products are evolved the loss may be obviated provided that before the products' are ablevto escape from the zone of treatment the evolved vapours are brought into contact with a zone of ore where reducing conditions exist.

According to the present'invention therefore aprocess for the recovery of tin from tin ores by chlorldization and volatilizationas stannous chloride is characterized by the fact thatthe ore is rst heated and partially reduced and thereafter the chloridizing agent is introduced to the heated and partially reduced ore.l

One form of the process for the recovery of tin from tin ores by chloridization and volatilization may be heated in admixture with solid carbona-I ceous material to effect the reduction and also to assist the chloridizing reaction.

Alternatively, or in addition, the outgoing vapours from the chloridizing furnace are caused to` pass through or over. a portion of ore which has already been heated and reduced, for example partially chloridized ore. This facilitates the applicationof the process as a continuous process in a rotating tubular furnace in which case the ore may be continuously introduced into and carried through a treatment furnace wherein the chloridizaton reaction is caused to occur and the Volatile reaction products are caused `to pass through the furnace along with the ore and removed at or near the place of removal. of the ore. When the ore is of a basic nature chloridization may conveniently be eected with the aid of a chloride such as calcium or ferrous chloride. 'I'he following is a description by way of example of a test in accordance with the invention:-

The ore employed was a naturally occurring sample from Siam. Complete analysis showed it to consist of:-.SiOa-l9.4%; -Snor-5.47% (Sn-4.308%); Fe2O3-53.35%; FeG-0.4%;

500 grammes of this ore were heated to 800 C. v

in a laboratory furnace of cylindrical type revolving at aspeed of one revolution in forty-ve seconds. To'the hot ore was added 10 grammes (2%) of charcoal crushed, to fifth inch and a period of ten minutes allowed for preliminary reduction to take place. A mixture of grammes (12%) ofcrushed crystalline ferrous chloride with a further 20 grammes (4%) of charcoal was then added. Evolution of stannous chloridew'as rapid at rst and appeared complete in less. than one hour. The temperature was maintained between 800Y to 820'C. for one and a half hours after which the ends of the reaction -chamber were closed and the :harge allowed to cool.

The residue weighed 412 grammes and assayed 0.56% of tin, the indicated extraction being 89.3% of the -tin originally present.

In the above example the ratio of chloride` used to chlorine theoretically required to coming taken 'from the same bulk samples. ThisV mixture was heated to about 800 to 810 C. for

twohours in a closed re-clay crucible provided with a vent hole. 'I'he hole was then closed `and the charge cooled. The residues weighed 412 parts and assayed 226% of tin. The indicated extraction in this case was only 56.8%

of the total original tin contents of the ore.

The accompanying drawing Ais a purely diagrammatic f representation of one form of apparatus for carrying finto effect the process according to the invention vin a continuous manner.

` ing therein through which` A munie chamber lf-of small cylindrical cross section relativelylto its. length is divided into two sections 2 and 3 -both of which are supported for rotation upon-rollers l. Sections 2I and 3 vare connected by anjintermediate stationary section 5 provided with-seals to' form a gas-tight joint whilst yet permitting rotation ofA sections z and s driven by amable niet-nannte. frire-ends of the chamber arejciosed-by nxedcoyers s and I also having gasgtight connectionto .the

rotatable sections. The muille Ais posed at a slight the co'vjer iA at the upper end of oredewY livery chute '3. Owil'igto.v tionand rotation of the munie ich the` lower end of'the mame in wellknown manner. `Oil burners'lfo'rV other suitable means are provided-for. heatingf-the two sections 0f the muiile, and the ore dungg'fits passage through section 2 becomes partiallyjreduced and preheatedto a high A' reagent in- 1er Il opens into the munie` from me intermediate section 5 and a chloridizing agent, for example.

'calcium chloride is admitted therethrough from a hopper Il at a predetermined rate set by a screw conveyor l2 which also forms a gas-tight seal. In its continued passage down the munie the ore is thus mixed with the chloridizing agent and the volatile products ofthe reaction pass along with the treated ore and are carried away through a port I3 in cover 1`to suitable condensing and scrubbing apparatus. The reduced ore finally emerges from the lriuille through an exit port I4 and the issuing material may serve as a self-seal to the volatile reaction products, and

is carried away upon a conveyor l5.

It is possible that in continuous operation as Just described the step of adding the carbon rst and deferring the addition of the chloridizingagentuntiltheorehasbeenpartiallyprereduced may in some casesbe eliminated, since the evolved vapours are led through or over parts of the ore which have already undergone the heat treatment and which will therefore be partially reduced and will thus absorb any chlorine carrying vapors other than fstannous chloride which may have been produced in the earlier stages. f' 4 1. A process for the extraction of tin from tin ores containing iron oxides by chloridization and volatilization as stannous chloride" wherein the ore is first heated with a reducing agent at such fhasan open-fi' ber' rewhlcn isfgintroduced through chute l atja rate admixed with a controlled-amount of car-v -bonaceous material will be fed'towards a `temperature that the iron oxide is reduced to v a'lower state of oxidation while leaving the tin oxide unreduced, and thereafter a normally solid chloridizing agent is introduced to the partially' reduced ore while the latter is'still heatedv and heating is continued at over 600? C. so that volatile reaction products are collected containing stan-l nous chloride and this is then separated from the products.

2. A process for the extraction of tin from tin ores containing iron oxide by chloridization and volatilization as stannous chloride wherein the ore is admixed with solid carbonaceous material,

then heated so that the iron oxide is partially` reduced by the action of the carbonaceous constituent while leaving the tin. unreduced and thereafter a normally solid chlorldizing agent is introduced to the partially reduced ore while the latterV is still hot and heating is continued at over 600 C. so that volatile reaction' products containing stannous chloride are given oil', these are collected and stannous chloride separated therefrom.

3. A process for the cintraction of tin from tin ores containing iron oxide by chloridization and volatilizaton as stannouschloride wherein ore is continuously introduced into and carried through a treatment furnace `where it is rst heated to a temperature adequate to. effect partial reduc` tion of the iron oxide without reducing the tin. a normally solid chloridizing agent is added to the heated and partially reduced ore, to eect the chloridization reaction while the ore is still only part-way through the furnace, and volatile products from the reaction are caused to pass along with the ore and are removed at or near the place of removal of vthe ore fromthe furnace.

4. A process for the extraction of tin from tin ores as claimed in claim lwherein chloridization is eifected with the aid of calcium chloride.

5. A process for the extraction of tin from tin ores as claimed in claim 3 wherein chloridimtion is effected with the aid of'calcium chloride.

6. A process for the extraction of tin from tin ores containing iron oxide -by chloridization and volatilization as stannous chloride wherein ore is continuously introduced into and carried through a treatment furnace where it is r'st heated to a temperature adequate to effect partial reductionof the iron oxide without reducing the tin, thereafter a normally solid chloridizing agent and a normally solid reducing agent are added to the partially reduced ore to eifect the chloridization reaction while the ore is still only part-way through the furnace, and volatile prod` ucts from the reaction are caused to pass along with the ore and removed at or near the place 1 of removal of the ore from the furnace.

is enacted by the employment .ssamm-mixing agent of ferrous chloride.

10. A process for the extraction oftin frorntiriv ores as claimed in claim 6 wherein chloridizatlon is effected by' the employment as chlorldizlng agent of ferrous chloride.

LOUIS ALBERT WOOD. 

